Bioethanol, which is an alternative liquid fuel, can be produced by ethanol fermentation of a fruit juice residue extract by yeast added thereto. Such a technique for converting a juice residue extract, or waste, to bioethanol by fermentation is very useful because biomass not competing with food is used as a starting material. In one known ethanol production technique using such a juice residue extract, the juice residue extract is produced from a citrus fruit and concentrated by, for example, centrifugation to obtain a citrus syrup. Then pulp is removed from the citrus syrup, and the resultant citrus syrup is subjected to ethanol fermentation by Saccharomyces yeast or the like (see, for example, Patent Literature 1).